Excel – Change Units of Measurement to Inches, Centimeters or Milimeters
By default, Excel takes units of measurement from the system settings. Sometimes, however, these settings are not the ones we want to use in Excel. The good news is that these units can be changed in Excel settings without having to intervene in the system configuration. Here's how to do it.
On the ribbon click File tab
On the left bottom, click Options
In Excel Options window go to Advanced options.
There in Display section is a Ruler units drop down. Click it and choose the unit you want.